I think there probably are times when people are deliberately being rude, but it doesn't sound like this is one of them. And most of the time, you don't know if they are, so better to assume that they aren't - frankly, most people don't going around trying to offend people that they actually like and want at their weddings, so chances are higher that it's not deliberate rudeness. Life is much easier if you don't assume someone is being rude and just try to see the best of it whether it's actually the case or not. If they are deliberately trying to piss you off, then I'm sure they'll have another go!
And yes, it doesn't mean one way is right and the other wrong - which is why you can't assume that someone is being rude for not inviting a partner, or for deciding that they won't invite you at all because they can't invite your partner, or not inviting you because they've felt they have to invite someone else's partner, or whatever. Just different ways of doing things. So the OP can feel disappointed, absolutely - nothing wrong with that - but no reason to assume that it's somehow the height of rudeness for her partner not to be invited.
What does it being after Xmas, or cash presents, or the middle of nowhere have to do with anything? You could well be happy to visit your parents/siblings then. It's in the middle of nowhere for everyone, not just you, so you are still arranging lifts with your partner or your siblings or whatever. If you don't actually want to go without your partner, then just don't!
Suggesting it's just 'fun' to read the posts trying to explain another side to it sound like you are still convinced that she is being rude and shouldn't have don't it, rather than just understanding that it's how she chose to do it, and it's not what you wanted, which is disappointing when you were looking forward to it. But not particularly wrong or inconsiderate.